Many processes are known for effecting an intimate mixture between otherwise immiscible fluids of relatively different specific gravities wherein such fluids are reacted or treated with each other. Such mixing is important, for example, to achieve a mass transfer of constituents from the fluid to be treated to the treating fluid.
Such liquid-liquid contacting processes are used extensively in industrial liquid-liquid or solvent extraction processes or in reactions wherein two or more substantially immiscible liquids, typically a hydrophobic organic liquid and an aqueous solution, are mixed together and one or more constituents from one of the liquid phases transfers to another liquid phase or is reacted with a constituent in another liquid phase. After the transfer has taken place, the intimately mixed phases are allowed to separate through a difference in their specific gravities. The mixing-settling process is usually repeated in a plurality of steps with countercurrent flow of the liquids to insure a maximum mass transfer or reaction of constituents therebetween.
A mixing-settling process is described, for example, in U.S. Pat. No. 2,077,057 wherein solvent extraction of mixtures of hydrocarbons is effected by mixing a light and heavy phase material, e.g., a solvent phase and an oil phase, in conjunction with a series of vertical separators having a plurality of baffles or partitions. In like manner, U.S. Pat. No. 2,144,797 describes a process for separating different constituents of oils wherein counterflowing streams of oil and solvent are divided into numerous relatively thin layers by use of multiple alternating baffle plates, said streams flowing rapidly in opposite directions to produce frequent mixing of layers as they move in intersecting paths at relatively high speeds followed by corresponding frequent settling at lower speeds. Further, U.S. Pat. No. 4,292,277 discloses a multistage co- or counter-current liquid extraction process comprising combination mixing-settling chambers having multiple upper and lower settling chambers separated from the mixing chamber by multiple upper and lower baffles. Other examples of such processes employ tray or packed separating towers, multiple-mixer settlers and the like.
Processes such as described above, however, often require significant capital and operating costs due to their elaborate labyrinthine configurations which, as shown, typically require a multitude of chambers and baffles. Further, in solvent extraction applications, such processes usually require large amounts of treating fluids, e.g., aqueous-based liquids, as such process typically do not provide for recycling of treating fluids. This further detracts from the efficiency of such processes as the extracting ability of the treating fluids or the reaction processes of constituents between two fluids cannot be readily optimized due to equilibrium conditions between the fluids to be treated with one another not usually being maximized during such finite contacting times.